1. Field of the Invention
This invention relates to a perforated tray column without downcomer formed by setting perforated tray without downcomers in place and a method for distillation by the use of the perforated tray column without downcomer. More particularly, this invention relates to a perforated tray column without downcomer equipped with in place such perforated tray without downcomers in order to effectively prevent the formation of a polymer of an easily polymerizable compound such as (meth)acrylic acid or a liquid containing such an easily polymerizable compound (hereinafter occasionally represented simply as “easily polymerizable compounds”) and allow an easily polymerizable compound to be distilled stably for a long time and a method for performing the distillation by the use of the perforated tray column without downcomer.
2. Description of the Related Art
Concerning such easily polymerizable compounds as (meth)acrylic acid and esters thereof, the distilling and rectifying such an easily polymerizable compound in the presence of oxygen or a polymerization inhibitor with the object of preventing the compound from polymerization has been heretofore practiced widely on a commercial scale. It has been also known to employ for this distillation perforated tray without downcomers and a perforated tray column without downcomer formed of these trays.
The perforated tray without downcomers used in the perforated tray column without downcomer each have holes formed nearly uniformly throughout the entire surface except those holes for clamps and bolts which are used in fixing the trays in conjunction with support beams and support rings. Since these perforated trays without downcomer are fixed with clamps and bolts inside the perforated tray column without downcomer generally in a divided pattern, they give rise to portions having no hole by reason of construction. Thus, a discrepancy arises between an actual opening ratio of the perforated tray of the column and an opening ratio of holes per unit area of the perforated tray.
When a perforated tray column without downcomer formed by setting in place such perforated trays without downcomer as revealing this discrepancy in an unduly large magnitude is used in distilling (meth)acrylic acid, for example, it encounters the problem that the efficiency of separation in the operation of distillation is lowered as compared with a counterpart having a smaller discrepancy. When the discrepancy is large, the distillation of (meth)acrylic acid, for example, performed with the wireless perforated tray column formed by setting in place perforated trays without downcomer of this large discrepancy entails the problem that since the operation possibly forms a polymer, it must be suspended to allow artificial or chemical removal of the polymer from the column.
The present inventors have proposed in U.S. Pat. No. 6,214,174, as a means to prevent the formation of a polymer during the distillation of (meth)acrylic acid, for example, even when the discrepancy revealed by the column in use is large, a method for promoting the prevention of the polymerization by providing perforated tray support members with openings adapted to preclude stagnation of a liquid on the support members. They have proposed in European Patent No. 1,029,573A2 a method for preventing the polymerization by specifying the diameter of holes in a perforated tray without downcomer, the distance between the centers of holes, the thickness of perforated trays, the opening ratio of holes, and the interval between adjacent perforated trays thereby preventing a liquid and a gas from channeling and imparting improved dispersibility thereto.
They, however, have been unable to discover a means which is effective in decreasing the discrepancy itself which arises between an actual opening ratio of the perforated tray of the column and an opening ratio of holes per unit area of the perforated tray.